The siblings enter the Catacombs with Nellie and find a tunnel network lined with stacked human bones and skulls. Amy looks for older skulls from Franklin’s time in Paris. Nellie leads them down a dark corridor using her keychain flashlight. Dan finds a strange array of skulls with numbers on them. Amy realizes it is a “magic box,” a kind of number game Benjamin Franklin invented that resembles sudoku, but this magic box is missing three numbers. Amy realizes that the missing numbers must be coordinates leading to the location of the next clue.

Suddenly Ian and Natalie ambush them. Amy threatens to destroy the skulls before the Kabras can copy down the numbers. Alistair Oh appears and tackles Natalie before she can shoot Amy with her dart gun.

Dan, Amy, and Nellie flee through the tunnels. They end up in a train tunnel with a train barreling toward them. Dan’s backpack gets stuck in the tracks, and he is unable to pull it loose. Amy pulls him out in the nick of time as the train sweeps away his backpack with the photo of his parents inside. Dan cries and Amy comforts him.